Exceptions

Introduction

• Exceptions are a mechanism to detect and handle errors without writing special code to test return values.
• Error handling code for common errors can be handled in a single place.

Structure

• A try clause has to have either a catch clause or a finally clause or both.
• catch must follow try.
• finally must follow the last catch clause.

Exception Hierarchy

• All exception classes are subtypes of java.lang.Exception.
• RunTimeException is a subtype of Exception which represents unchecked exceptions. All unchecked exception will inherit from this class.
• Classes which derive from java.lang.Error indicate serious problems that an application should not try to catch. e.g OutOfMemory error.
• Both Error and Exception classes are derived from the java.lang.Throwable class.

Exception Handling

• The order of catch clauses is important.
• If the exceptions are in the same class hierarchy, The most-specific exception type should be first, followed by the more general exceptions. Otherwise, the code will not compile.
• If exceptions are in different class hierarchy, then the order does not matter.
• Each method must follow the handle or declare law for checked exceptions.